Permeable sheets of filtration media are used widely to remove contaminants from fluid streams and in order to achieve optimal performance of the filtration media, the surface of the sheet that is exposed to the fluid stream needs to be large, but in order to avoid excessive size of filtration elements, the sheets need to fit into small volumes and are typically pleated to maximize the ratios between filtration surfaces exposed to the fluid streams and the overall dimensions of the filtration elements.
When exposed to fluid steams, these filtration elements and the permeable sheets in them are exposed to forces from the fluid streams and need to withstand these forces sufficiently to ensure continued acceptable operation of the filter element. In particular, pleated sheets of permeable filtration media are often prone to deflection and adjacent sheets are often too close together or touch and thus prevent a well dispersed flow pattern of the fluid—and reduce the available surface area of the filtration media for loading—a phenomenon known as “masking”. Further, in order to be cost effective, filtration elements made from sheets of permeable filtration media typically do not include structural supports for the filtration media, but rely on the structural integrity of the folded sheets themselves.
Pleated filtration media are typically formed from continuous or rolled webs and pleats are formed perpendicular to the “machine” or “reel” direction of the media, i.e. to the continuous direction of the media as it comes from a source, such as a supply reel. Simple alternating “zigzag” pleats are commonly used and are simple to form, but are prone to deflection and masking, especially in cases of deep pleats. Some methods have been proposed to inhibit deflection and/or retain spacing between adjacent pleats, but these methods tend to require complex (and thus costly) manufacturing methods (e.g. because they require adjacent layers of pleated filtration media to be attached together with adhesive), they are not versatile because their geometry is static, and/or they are prone to crushing and collapsing. The present disclosure seeks to address at least some of the challenges mentioned above and in particular to provide elements of folded sheet material with improved structural stiffness, flexibility and compressibility, or maximizing surface area, which can be manufactured cost-effectively.
Some techniques used previously include those described in U.S. Pat. No. 2,683,537 and U.S. Pat. No. 5,522,909, incorporated by reference herein.